The invention resides in the field of air pollution abatement by oxidation of the objectionable constituents in a gaseous emission. Oxidation is brought about through scrubbing liquid-gas contact in a bed of packing material. The odorous, contaminated gas flows upwardly through the packed bed while the scrubbing liquid, the oxidizing agent in aqueous solution, flows or trickles downwardly over the packed bed.
An aqueous solution of potassium permanganate has long been recognized as an odor controlling agent. The chemical reaction may be expressed generally as follows: EQU 2KMnO.sub.4 + H.sub.2 O .fwdarw. 2KOH + 2MnO.sub.2 + 3O EQU O + odorous constituents .fwdarw. HCO.sub.3.sup.-
a process based upon potassium permanganate for controlling odors in an environment similar to that contemplated by the present invention is described in an article by Posselt and Reidies entitled "Odor Abatement with Potassium Permanganate Solutions" published by I & CE Product Research and Development, in Volume 4, No. 1, March 1965. Apparatus for achieving scrubbing liquid-gas contact with opposing flow through a bed of packing material is shown in the Blanding U.S. patent (No. 2,321,455) issued on Nov. 25, 1947.
In normal practice a solution of water and dissolved oxidizing agent is pumped to the top of a chamber and then flows by gravity through a packed bed. This scrubbing solution is collected in a holding tank and then recycled through the packed bed. Gases absorbed at the liquid-gas interface are oxidized by the chemical. Unfortunately, organic and other oxidizable particulate matter collected in the liquid are also oxidizable. Since the solution is being recycled, particulate matter consumes oxidizing agent on a continuing basis.
The oxidation of dissolved gases (vapors) present as solutes in the scrubbing solution requires a short time and low concentration of oxidizing agent, whereas the oxidation of suspended solids requires relatively longer times and high concentrations of oxidizing agent. Consequently, the continual recycling of a solution containing excess oxidizing agent and non-purged particulate matter results in needless consumption of the oxidizing agent in the complete oxidation of the particulate matter.
Thus, the problem with the prior art process is cost. The primary cost factor in using a chemical oxidizing agent, where the oxidizing agent is dissolved in the carrier liquid, is the high consumption rate and, therefore, high operating cost due to high consumption of the oxidizing agent. The consumption rate is far in excess of that theoretically necessary to oxidize only the gaseous impurities in the treated air stream being cleaned or purified. An excessive amount of oxidizing agent must be continuously added to oxidize the odorous constituents This high consumption rate of the oxidizing agent makes the economics of operating according to the prior art unattractive.